I don't understand why this matters. You were asking for a reason, that's the reason. You can call it a "thin excuse", but Mullenweg's been upfront about his position.
> Seems like a pretty thin excuse for taking 8% of gross revenue.
The 8% comes from the trademark licensing agreement [0]. They also offer to put them in the Five for the Future program if they do the contribution (they can also spend that 8% on people working on WordPress, which again enriches Mullenweg not at all, or some combo). This sounds pretty clearly like it's addressing the "you contribute very little back to the community" criticism Mullenweg has.
There's even more evidence in the "Forking" section, where they're basically like, "quit switching the attribution codes on our stuff".
Again, it sounds like WP Engine was being pretty uncool, and Mullenweg's trying to get them to be cooler.
define( 'WP_POST_REVISIONS', false );
Seems like a pretty thin excuse for taking 8% of gross revenue.
What other unspoken rules are there lurking behind "don't turn off revision tracking"?